Process of forming colored anode oxidized film on aluminummaterial

ABSTRACT

PROCESS FOR FORMING COLORED ANODE-OXIDIZED FILM ON AN ALUMINUM MATERIAL BY SUBJECTING THE ALUMINUM TO ANODIC OXIDATION IN AN AQUEOUS SOLUTION CONTAINING A MAJOR PROPORTION OF OXALIC ACID AND A CHLORINE COMPOUND AND IN SOME CASES, AT LEAST ONE OR MORE COLOR CONTROLLING AGENTS, WITH APPLICATION OF EITHER AN ELECTRIC CURRENT HAVING AN EXCESSIVE A.C. COMPONENT OR AN ELECTRIC CURRENT HAVING AN EXCESSIVE D.C. COMPONENT. WHEN AN ELECTRIC CURRENT HAVING EXCESSIVE D.C. COMPONENT IS USED, A PREVIOUS ELECTROLYSIS IS CARRIED OUT PRIOR TO THE ANODIC OXIDATION.

United States Patent 3,654,100 PROCESS OF FORMING COLORED, ANODE OXI- DIZED FILM N ALUMINUM MATERHAL Kazuko Nagai, Yokohama, and Yoshiliaru Yamada, Kawasaki, Japan, assignors to Rilten Ainnte Industry Co.,- Ltd., Kawasaki, Japan No Drawing. Filed May 25, 1970, Ser. No. 40,411 Claims priority, application Japan, May 31, 1969, 44/4 208 Int. or. can */02 US. Cl. 204-35 N 5 Ciaims ABSTRACT OF THE DISCLOSURE This invention related to a process of forming a colored, anode-oxidized film on an aluminum material.

In known processes for forming colored surfaces the aluminum material is usually subjected to anodic oxidation by the use of electrolytic solutions containing mainly a sulfonic acid-type compound as shown in following Table 1.

Table 1.Compositions of electrorllvgtifigogth in known electrolytic coloring Amount Number Composition (percent) 1 {Sulfosalicylic acid -15 Sulfuric acid 1-2 Sulfosalicylic acid. 1-5

2 Sulfuric acid 0. 1-1 Maleic acid 0.11.5

3 {Suliophthalatm 10 Sulfuric acid. 0. 1-2

4 {Phenolsulfonic ac 10-20 Sulfuric acid 0. 5-2

When using an electrolytic solution containing mainly a sulfonic acid-type compound such as described 1n the above Table 1, aluminum particles or residue produced in the electrolytic bath throughout the operation may be removed by a subsequent step, such as an ion exchange treatment. This enables the concentration of aluminum in the electrolytic bath to be retained at a lower concentration, for example, of less than 3 to S g./l.

Also, if the aluminum particles concentration in the electrolytic bath is increased to more than the values mentioned above, the coloring is difficult to produce on the aluminum material. Furthermore, disadvantageously, the sulfonic compound itself used in the prior art processes is expensive.

An object of this invention is to eliminate the foregoing disadvantages of the prior art processes, and to provide a new process wherein a colored film which excels in color fastness and other physical properties, can be obtained simply, effectively and relatively inexpensively.

The foregoing and other objects are attained in applicants invention, which illustratively comprises a process for coloring aluminum material, in which an anodicoxidation reaction is accomplished with the use of novel alternating current and direct current combinations in an oxalic acid bath having chlorine ions therein. The anodic ice oxidation reaction is carried out in an electrolytic bath or solution comprising an aqueous solution containing mainly an oxalic acid, which is widely used in conventional anodic oxidation of the aluminum material, and a chlorine compound, which was found to increase the electric conductivity of the bath or solution and the resulting film, and to accelerate the anodic oxidation reaction. In some cases, where desirable, a color controlling or promoting agent which is able to change the color tone may be added.

According to the present invention, aluminum or aluminum based material or alloy, hereafter referred to as aluminum material is subjected to an anodic oxidation process in the aqueous solution with use of an electric current which may be either an electric current having AC and DC components in which the DC component is greater than the AC component or having only DC component, and selected from the following (a) a superposition of alternating current and interrupted direct current, (b) an alternate use of alternating current and direct current and (c) an interrupted direct current only, or an electr1c current having AC and DC components in which the AC component is greater than the DC component or having only AC component, and selected from the following (d) a superposition of alternating current and direct current and (e) an alternating current only.

When the anodic oxidation is carried out using an electric current having excessive DC component, such as the electric current, (a) (b) and (c) mentioned above, an electrolysis must be carried out prior to the anodic oxidation. The previous electrolysis may be carried out in a dilute oxalicor sulfuric-acid solution or any other electrolytic solution which is able to carry out the anodic oxidation.

On the other hand, when the anodic oxidation is carried out using an electric current having excessive AC component, such as the electric currents (d) and (e) mentloned above, no previous electrolysis need to be used.

In one embodiment of the invention, for example, the aluminum material is subjected to a previous electrolysis in a 4% oxalic acid solution (which does not contain chlorine ion) for a period of from about 10 sec. to about 3 min. with AC current having a current density of from about 0.2 to about 1 a./dm. It is then subjected, for a period of time which depends on the color and film characteristics desired, to anodic oxidation in an electrolytic solution containing mainly or a substantial portion of oxalic acid and from about 0.05 g./l. to about 1 g./l. of chlorine ion, such as in the form of NaCl, and from about 0.3 g./l. to about 10 g./l. of sulfuric acid and if necessary, at least one or more color controlling agents, with the electric current above mentioned having an excessive DC component.

In another embodiment of the invention, for example, the aluminum material is subjected to anodic oxidation in an electrolytic solution which is the same as used in the above-mentioned first embodiment using the abovementioned electric current having an excessive AC component, without first subjecting the aluminum material to a previous electrolysis step as done in the first embodiment.

Generally, the variation of the resulting color depends upon the ratio of DC and AC components of the electric current, even if the electrolytic baths which are used have the same composition.

The typical color tones obtained in the present invention are shown in Tables 4 and 6. When only AC current is used, the color tone has a tendency to develop a light gray. In this case, for example, the AC current had a current density of 2 a./dm. and a voltage of from 60 volts to volts.

The electrolytic solution which is used in the anodic oxidation contains chlorine ions, such as supplied by a chlorine containing compound. Suitable chlorine com- 60 C. for about 1 min. and subsequently Washed with pounds may be, for example, potassium chloride, sodium water. chloride, magnesium chloride, calcium chloride, hydro- Neutralization: The degreased samples were immersed chloric acid, potassium chlorate, potassium perchlorate, in a 10% nitric acid solution at about room temperature etc. for about 30 sec. and subsequently washed with water.

The color tone and the thickness of the resulting colored The samples, which were pretreated in the above manfilm depend on the kinds of color controlling agent and ner, were then subjected to electrolysis in a dilute oxalic he am un s of t r n compound Which are used, acid solution having A.C. current applied thereto, which and also the ratio of DC and AC components of the had a current density of from 0.2 to 1 a./dm. at about electric current. room temerature for about 30 sec.

The amount of chlorine compound used may be from The electrolyzed aluminum material samples were then to 10 and Preferably from t0 5 g subjected to anodic oxidation in each electrolytic solu- In the above-mentioned electrolytic Solut o Which is tion as mentioned in the following Table 3 with the superused in the an0di X t a 60101 Controlling agent position of AC. current having a current density of from y be used if necessary The Controlling agent y 1 to 1.5 a./dm. and a voltage of up to 60 volts and inp Sulfuric acid Compound Such as Sulfuric terrupted DC. current having a current density of from acid, sodium sulfate etc., a sulfonic acid compound such 3 to 35 and a voltage of up to 70 volts and at a as sulfonic acid, sodium sulfonate etc., a carboxylic acid temperature f 15 C fo a i d of about 50 Compound Such as formic acid, acetic acid P min. When the direct current was intermittently applied, Phoric acid Compound Such as Phosphoric acid, Sodium the direct current passed through for about 60 sec. and sub- Phosphate and a thiocyanic acid compound Such as sequently interrupted about 10 sec. during the operation. potassium thiocyanate etc.

The chlorine compound and the color controlling agent TABLE 3 may be used in such amount that the anodic oxidation in Electrolytic bath composition the electrolytic solution containing oxalic acid is not ob- Free Reducing structed. Thus, the amount of color controlling agent can oxalic c m n n 01-, other preferably be, for example, from 0.1 to 100 g./l. i -l s-l g-l eddltlve, al

Also, when using interrupted DC, for example, the 40 90 15 direct current may be intermittently applied in such mani8 38 8% g. ner that the direct current flows for about 2 0 to 120 sec., 40 90 S-ummc acid 4 preferably about 60 sec. and subsequently interrupted for 2g 38 8.2% 3 about 1 to sec., preferably about 10 sec. during the 40 90 soda a g operation. 40 00 0.30 Sulfosalieylie acid 10. The time required for the above-mentioned electrolysis 40 90 40 Acetic acid N nd step may range from about 10 to about 3 mm a Amount of reducing component (g./l.) was represented as oxalic acid.

Preferably 30 to 60 2 NaOlwas added as 01- ion.

The inventive process, which is simple and inexpensive, produces an x elle t colored aluminum having a good The resulting anodic oxldized materials were then light and weather resistance, corrosion resistance and abra- Washed W th Water, Immersed in a 10% nitric acid solusion resistance. Also advantageously, conventional alumi- 40 9 at room temperature for about 30 560-, Washed agalfl Hum i l h as aluminum l i b d or 1 with water and then sealed with steam having the presminum alloyed material, such as shown in the following sure of from about 3 to 4 g/ for about 20 min. Table 2, can be used. No special material is necessary to The physical properties of the colored films obtained in perform the inventive process. this Example 1 are shown 1n the following Table 4:

TABLE 4 Corrosion Abrasion Sample Thick- Hardness resistance resistance 0. Color tone ness (HmV) (sea) (sea) 1 Brown olive 450-480 600-700 10-11,000

Black (sepla series) lack 0. k 45 450-480 700-800 13-141000 10 Dark yellow 28 430-460 600-700 6-7,o00

The invention will be illustrated by the following ex- In the above table, the hardness was determined by a amples but not restricted only to those examples. micro-hardness meter with a load of g. The corrosion The compositions of the aluminum material used in the resistance was determined by the dropping method using examples are discussed in the following Table 2. a 10% caustic soda solution at 35 C.:1 C. The abra- TABLE 2 Compositions (percent) Sample No. Al Sn Fe Cu Mn Mg Cr Zn Ti 7 1,0 0. 20 0. 05 0. 01 iji lili' III 25332 0. 2 5 0.35 0.10 0.10 0. 45-00 0.10 0.10 0.10

EXAMPLE 1 sion resistance was determined according to JISH8601 First, various samples of the aluminum material No. (Japanfise Industrial Standard)- Sample e 1100 mentioned in the above Table 2 were pretreated as ored films obtained under the conditions of this Example follows: 1 according to the present invention. Sample No. 10 is a t g fi gg f g igi f ggc gi g i control or contrast sample of colored film obtained by su u 1c and washed with water, after which the treated samples using a 4% oxalic acid electrolyte according to the were immersed in a 10% caustic soda solution at about ventional prior art method.

As is evident from Table 4, the thickness and the abrasion resistance of the colored aluminum material obtained using the present invention, are increased substantially, in comparison with those obtained according to the conventional prior art method.

Furthermore, the colored films obtained with the present invention, did not crack during the sealing treatment, even though its thickness increased substantially.

EXAMPLE 2 First, various samples of the aluminum material No. 6063 described in Table 2 were pretreated as follows:

Degreasing: The samples were immersed in a 10% sulfuric acid solution at about 80 C. for about 1 min., washed with water, after which the treated samples were immersed in a 10% caustic soda solution at about 60 C. for about 1 min. and then washed again with water.

Neutralization: The degreased samples were immersed in a 10% nitric acid solution at about room temperature for about 30 sec. and then washed with water.

The pretreated samples were then subjected to anodic oxidation in each of the electrolytic solutions described in the following Table 5, with the superimposition of AC. current having a current density of about 2 to 3 a./dm. and a voltage up to 80 volts, and D.C. current having a current density of about 1 to 1.5 a./dm. and voltage up to 44 volts at a temperature of 15: 1 C. for about 50 min.

TABLE 5 Electrolytic bath composition Free Reducing oxalic component Cl Other Sample No. acid, g./l. g./l. g./l. additive, g./l.

40 90 0.43 Sulfuric acid 3.

40 90 0. 30 Rhodan potash 3. 40 90 0. 40 Formic acid 15.

40 90 0.30 Phosphoric acid 10. 40 90 0. 30 Trichloro acetate 5.

1 Amont of reducing component (g./l.) was represented as oxalic acid. 2 NaCl was added as Cl" ion.

The resulting anodic oxidized materials were washed with water, immersed in a nitric acid solution at room temperature for about 30 sec., washed with water and then sealed with steam at a pressure of from 3 to 4 kg./cm. for about 20 min.

The physical properties of the result colored films obtained in this Example 2, are shown in the following Table 6:

Various modifications and extensions of this invention will become evident to those skilled in the art. All such modifications, variations and deivations, which basically rely on the teaching through which this invention has advanced the art, are properly considered within the spirit and scope of the invention.

What we claim is:

1. Process of coloring a surface of an aluminum material comprising the steps of subjecting said aluminum material surface to anodic oxidation in an electrolytic solution containing a substantial portion of oxalic acid, and a chlorine compound in an amount of from 0.01 g./l. to 5 g./l. and using an electric current having an AC component and a DC component, said DC component being greater than said AC component and having a current density of from 3 a./clm. to 3.5 a./dm. and said AC component having a current density of from 1 a./dm. to 1.5 a./dm.

2. Process according to claim 1. wherein said electric current is only a combination of AC and interrupted DC.

3. Process according to claim 1, wherein said electrolytic solution further contains one or more color promoting agents.

4. Process of claim 1, wherein a previous separate anodic oxidation step is carried out prior to said anodic oxidation step.

5. Process of coloring a surface of an aluminum material comprising the steps of subjecting said aluminum material surface to anodic oxidation in an electrolytic solution containing a substantial portion of oxalic acid and a chlorine compound in an amount of from 0.01 g./l. to 5 g./l. and using an electric current having AC and DC components, said AC component being greater than said DC component and having a current density of 2 to 3 a./dm. and said DC component having a current density of from 1 a./dm. to 1.5 a./dm.

References Cited UNITED STATES PATENTS 2,685,563 8/ 1954 Gauthier 204-58 3,152,970 10/1964 Jensen 20435 N 3,382,160 5/1968 Asada 204-58 FOREIGN PATENTS 393,565 9/ 193 1 Great Britain 204-5 8 JOHN H. MACK, Primary Examiner W. I. SOLOMON, Assistant Examiner U.S. Cl. X.R. 204-58 

